An engine, such as an internal combustion engine, includes a crankshaft sensor and at least one camshaft sensor.
A crankshaft sensor comprises a crankshaft toothed wheel, rotating as one with the crankshaft and comprising a large number of regular teeth and at least one marker. The crankshaft sensor also comprises a crankshaft detector facing said crankshaft toothed wheel and able to detect a presence/absence of material and thus to detect a tooth or a gap.
The crankshaft toothed wheel is equally angularly divided into a large number of regular teeth, thus making it possible to accurately ascertain the angular position of the crankshaft. The crankshaft toothed wheel also comprises at least one marker, allowing a given angular position to be identified in absolute terms. Said marker is generally associated with one position of the engine, such as, conventionally, the top dead center of the first cylinder.
However, for a four-stroke engine, a crankshaft performs exactly two revolutions per engine cycle. Therefore, ascertaining the angular position of a marker indicates the angular position of the crankshaft but is not enough to indicate the angular position of the engine. That position is known with an uncertainty that is dependent on the product that is the number of markers on the crankshaft wheel multiplied by the number of crankshaft revolutions per engine cycle. Thus, with a crankshaft wheel that makes two revolutions per engine cycle and comprises a single marker, the uncertainty is by one marker in two.
At least one camshaft sensor can be used in addition, or as an alternative.
A camshaft sensor comprises a camshaft toothed wheel, rotating as one with a camshaft and comprising a small number of teeth that are advantageously irregular. The camshaft sensor also comprises a camshaft detector facing said camshaft toothed wheel and able to detect a presence/absence of material and thus to detect a tooth or a gap.
A camshaft performs exactly one revolution per engine cycle. The teeth of the camshaft toothed wheel generally display differences in tooth or gap length that allows them to be identified.
This means that, by cross-referencing the information from the crankshaft sensor and from the camshaft sensor(s), it is possible to determine exactly the angular position of the engine, modulo one engine cycle, namely modulo 720° CRK.
It is appropriate to draw a distinction between an exact synchronization method, which produces a precise angular position of the engine, and an estimated synchronization method, that produces an estimated interval assumed to contain the angular position.
Document FR 2 981 121, in the name of the Applicant Company, incorporated by reference herein, discloses an exact synchronization method, that determines an angular position modulo one crankshaft revolution, namely modulo 360°, using the marker present on the crankshaft toothed wheel, and removes any doubt as to which revolution according to the measurements of the angular lengths and/or positions of the teeth as indicated by a camshaft sensor. The principle behind this approach is to make assumptions regarding the angular position of the engine, as soon as a marker is observed, and to invalidate all the assumptions except for a final one progressively as the new events (“start of tooth”, “end of tooth”), mainly coming from the camshaft sensor, arise.
The chief disadvantage with this approach is the length of time it takes. This approach entails waiting for a marker which may require half an engine cycle, then receiving and processing events coming from the camshaft sensor until the superfluous assumptions can be eliminated. This approach typically converges toward an angular position of the engine after a rotation through 500° to 720° CRK.
Exact synchronization is needed in order to perform ignition.
Document FR 3 004 218, in the name of the Applicant Company, incorporated by reference herein, discloses an estimated synchronization method, that produces an estimated interval assumed to contain the angular position. That method uses all the events coming both from a crankshaft sensor (“marker”) and from at least one camshaft sensor (“start of tooth” and/or “end of tooth”) in order to identify at least one camshaft tooth profile as early on as possible. Here, all the available events are put to use, without necessarily waiting for a marker, in order to save time. In order to increase the number of events, several camshaft sensors are advantageously employed. This estimated synchronization method produces an estimated interval, which can be obtained very quickly, typically in under 360° CRK, but which may be discontinuous and/or exhibit a very broad angular span.
Injection, unlike ignition, can be performed as soon as the estimated interval is continuous and exhibits a sufficiently narrow span. Another patent application by the Applicant Company, filed on May 17, 2016, under number FR 1654361, incorporated by reference herein, allows an estimated interval to be rendered continuous.
To date, these two types of method have been used independently. On the one hand, an estimated synchronization method is used to determine the instant at which injection can be performed. On the other hand, an exact synchronization method is used to determine the instant at which ignition can be performed.
If ignition is not performed following injection, the fuel will be discharged, unburnt, in the next exhaust phase. In order to avoid such pollution, it is appropriate for exact synchronization that allows ignition, to be determined shortly after an estimated synchronization, that allows injection, has been determined. The maximum length of time between the availability of estimated synchronization and the availability of exact synchronization is typically of the order of 220° CRK.